1. Field of the Invention
The present invention generally relates to compounds that may be used to inhibit corrosion of metallic containers, such as those made of tin, aluminum, steel, or a combination thereof. More specifically, the present invention relates to such corrosion inhibiting compounds for use in cosmetics and other topically applied products.
2. Description of the Prior Art
Recent legislation and changing consumer preferences have lead to the development of cosmetics and other topically applied consumer products that have lower concentrations of volatile organic compounds (VOCs) compared to similar compositions of merely a decade ago. In general, newer compositions replace the less favored VOCs with water and/or other compounds, such as alcohol, that typically contain residual amounts of water. However, water creates a potential for metallic container corrosion that exponentially increases as the water content increases.
The mechanism of corrosion may be uniform, galvanic, intergranular, or concentrated. Such corrosion may manifest itself as crevice corrosion, pitting, selective leaching, or stress cracking. Corrosion usually occurs electrochemically, involving electron transfers away from metals that are being oxidized, and electron acceptance by substances that are reduced.
The main approaches to minimize corrosion from fluids in a metallic container are to (1) lower the concentration of oxygen, (2) lower the concentration of corrosive ions, such as chlorides and sulfates, (3) optimize the pH of the composition, (4) utilize corrosion inhibitors, and (5) use a combination of any or all of the previous four approaches.
Corrosion inhibitors may be used as a lining material on the inner surface of the metallic container or canister or may be incorporated into the composition. However, while corrosion inhibitors may reduce the rate of overall corrosion, the electrochemical conditions of the composition may shift such that stress corrosion cracking and/or pitting may occur.
Many corrosion inhibitors are unsuitable for use in cosmetics and other consumer product compositions because the corrosion inhibitors have an objectionable effect on the aesthetics and/or function of the composition in which it is incorporated. As an obvious example, chromates and dichromates are well known corrosion inhibitors, yet are very toxic to humans.
U.S. Pat. No. 3,992,318 to Gaupp, et al. describes a corrosion inhibitor that requires a combination of a water-soluble phosphonic acid or its salt, a water-soluble polyphosphate or alkali metal phosphate, and a water soluble polymer of acrylic acid and/or methacrylic acid. The Gaupp, et al. patent discloses that this corrosion inhibitor is suitable for aqueous systems, particularly cooling systems for heat-producing equipment.
U.S. Pat. No. 4,240,925 to Tait discloses a pitting corrosion inhibiting composition that requires a cathodic corrosion inhibitor that is a phosphoric acid ester, amide or amide-ester, and an anodic corrosion inhibitor that is an organic compound.
U.S. Pat. No. 4,052,160 to Cook, et al. discloses the use of phosphonocarboxylic acids as corrosion inhibitors and/or scale control agents.
U.S. Pat. No. 4,548,787 to Wilson et al. discloses compositions for inhibiting mineral scale and the corrosion of metals. The compositions have water-soluble salts of an acid that can be molybdic acid, tungstic acid, and selenic acids in combination with a water-soluble phosphate.
Czech Patent No. 262,475 describes single component varnishes that have, among other ingredients, Group II metal dihydrogen phosphates.
Czech Patent No. 244,376 describes corrosion inhibitors for closed water and water-alcohol cooling systems. The corrosion inhibitors have an inhibitor mixture that includes disodium hydrogen phosphate, sodium metasilicate, and 1,2,3-benzotriazole.
Chinese Application No. 1,103,655 describes an anticorrosive heat transfer composition for heat pipes. The composition has sodium hexametaphosphate, trisodium phosphate, and disodium hydrogen phosphate, among other ingredients.
There is a need for corrosion inhibitors for use in cosmetics and other consumer product compositions that are non-toxic, non-aromatic, invisible, and generally compatible with the extensive variety of compounds that are used in cosmetics and other consumer product compositions.
Applicants have surprising discovered that phosphate compositions may be used in cosmetics and other consumer product compositions to effectively inhibit corrosion, yet exhibit no undesirable aesthetic and/or functional attributes. Specifically, applicants have discovered that phosphates and/or polyphosphates are effective in cosmetics and other consumer product compositions when present in an amount about 0.05 percentage by weight (wt %) to about 1.5 wt % based on the total weight of the finished composition.